Biological Effects of Stroma-derived Factor-1 Alpha on Normal and CML CD34+ Haemopoietic Cells

We compared the biological effects of the CXC chemokine SDF-1alpha on immunomagnetically purified CD34+ cells isolated from human normal bone marrow (NBM), leukapheresis products (LP) and patients with chronic myeloid leukaemia (CML). LP CD34+ cells showed a significantly stronger migration response to SDF-1alpha (100 ng/ml) than CD34+ cells isolated from the peripheral blood (PB) of CML patients (P < 0.05). The chemotactic response to SDF-1alpha was also reduced in CML BM CD34+ cells in comparison to NBM CD34+ cells but the observed differences were not statistically significant. In analogy to normal CD34+ cells circulating CML PB CD34+ cells were less responsive to SDF-1alpha than their BM counterparts (P < 0.05). Furthermore, SDF-1alpha elicited similar concentration-dependent growth suppressive effects on normal and CML CD34+ cells (P > 0.05) in colony-forming cell assays. We then demonstrated that SDF-1alpha triggers intracellular calcium increases in CD34+ cells and there were no differences in the time course and dose response characteristics of normal and CML CD34+ cells. The reduced migration response to SDF-1alpha in CML CD34+ cells was not due to a down-regulation of the SDF-1alpha receptor CXCR-4 as flow cytometric analysis revealed similar CXCR-4 expression levels on NBM, LP, CML PB and CML BM CD34+ cells (P > 0.05). Finally, no differences in the modulation of CXCR-4 levels in response to SDF-1alpha and serum were observed in CML and normal CD34+ cells. Our data suggest that the impaired chemotactic response of CML CD34+ cells to SDF-1alpha is not caused by a lack or complete uncoupling of CXCR-4, but may be due to an intracellular signalling defect downstream of the receptor.